1. Technical Field
The present invention relates to a hard disk drive using a headerless servo format, and more particularly, relates to a method for organizing servo data and counting sector numbers from the headerless servo format without the need for a sector number region.
2. Related Art
Hard disk drives (HDD) typically include one or more magnetic disks defining a multiplicity of concentric data tracks. Each data track is divided into sectors with intersector gaps therebetween, and each sector is subdivided into a data section and a servo section. The data sections are used for the storage of main data or user information. The servo sectors are used for the storage of control data such as automatic gain control data, track addresses and tracking servo patterns for use in positioning a head. Magnetic disk drives having high data density generally rely upon servo control systems for moving a selected transducer (head) from a departure track to a destination track location when data information is written or read from the disk. Exemplary disk drive architectures having head position control systems using servo information are disclosed in U.S. Pat. No. 5,210,660 for Sectored Servo Independent Of Data Architecture issued to Hetzler, and U.S. Pat. No. 5,255,136 for High Capacity Submicro-Winchester Fixed Disk Drive issued to Machado et al., U.S. Pat. No. 5,475,540 for Magnetic Data Storage Disk Drive With Data Block Sequencing By Using ID Fields After Embedded Servo Sectors issued to Gold., and U.S. Pat. No. 5,596,460 for System And Method For Encoding A Servo Address issued to Greenberg et al.
A typical sector of an arbitray track of the magnetic disk is composed of a servo section in which servo information is recorded and a data section succeeding the servo section in which data identification (ID) is recorded. A conventional data section includes a plurality of identification (ID) regions, data regions and PAD regions serving as intersector gaps therebetween. Commonly, the ID region includes an ID sync, an ID address mark (AM), a head and cylinder number, a sector number, a split and flag, and a cyclic redundancy check code (CRC). The data region includes a data sync, a data address mark (AM), data and an error correction code (ECC). Generally, in order to read information of the ID region and the data region of the respective data section, the HDD must be synchronized with a clock frequency previously written on the magnetic disk by using the ID sync and data sync. In practice however, the ID sync requires many bytes that are restrictive for high density HDD application.
Recent efforts to formulate a headerless sector format suitable for high density HDDs are disclosed, for example, in U.S. Pat. No. 5,500,848 for Sector Servo Data Recording Disk Having Data Regions Without Identification (ID) Fields issued to Best et al, U.S. Pat. No. 5,523,903 for Sector Architecture For Fixed Block Disk Drive issued to Hetzler et al., U.S. Pat. No. 5,581,418 for Magnetic Disk Drive Unit Capable Of Determining Data Region Position Of Data Region That Does Not Include Position Identification Data issued to Hasebe, and U.S. Pat. No. 5,627,695 for System And Method For Generating Unique Sector Identifiers For An Identificationless Disk Format issued to Prins. Best et al. '848, for example, disclose a fixed block architecture sector format that includes information encoded in the servo region of a sector to enable a data recording head to locate and identify a data sector for read and write operations without the need of an ID region. Similarly, Hetzer et al. '903 and Hasebe '418 each discloses a sector architecture that further includes information contained in electronic storage to enable the data recording head to locate and identify data sectors for read and write operations without using data ID fields. Likewise, Prins '695 also discloses a disk drive system for determining a sector ID of a data sector on a disk without using data ID fields in order to maximize disk capacity.
Generally, the servo section of the HDD using a headerless servo format includes a preamble region for synchronizing with a system clock, a servo address mark (SAM) region for recording a reference pattern for producing various servo timing signals, an index (IDX) region for supplying single rotation information of the disks, a sector number region for recording a servo sector number, a head number region for recording the head number, a gray code region for recording trade information, a servo burst region for the on-track control of the heads and a postamble region.
Typically, index information consists of one bit, the sector number region consists of 7 bits, and the head number region consists of 2-3 bits all of which are varied depending on the capacity of the HDD. The purpose of using a headerless servo writing pattern is to remove data ID from the data section so as to increase the capacity of the data section. This headerless servo writing pattern, however, results in the increase of the servo section length due to the augmentation of the servo data. Moreover, if the servo data is erroneously written on the servo section, the accuracy of the servo data cannot be guaranteed.